<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /* 选择被勾选的复选框 */
    .ck:checked {
      width: 30px;
      height: 30px;
    }
  </style>
</head>

<body>
  <input type="checkbox" name="" id="" class="ck">
  <input type="checkbox" name="" id="" class="ck">
  <input type="checkbox" name="" id="" class="ck">
  <input type="checkbox" name="" id="" class="ck">
  <button>查看</button>

  <script>
   input:checked{
    width: 50px;
    height: 50px;
   }


  </script>

</body>

</html>